1. Field of the Invention
The invention relates to a device for depolymerizing used and waste plastics, and also to an associated process.
2. Discussion of the Background
In a process for re-treating carbon-containing waste, EP 0 236 701-A1 describes a thermal pretreatment in the presence or absence of hydrogen of organic wastes of synthetic origin as a preliminary stage for a subsequent hyrdogenating treatment. From the description and also from the examples it emerges that such a pretreatment can be carried out in a stirred reactor.
EP 0 512 482 A2 describes a thermal treatment of such synthetic organic wastes in which no coke formation or only a small amount of coke formation occurs in the absence of hydrogen.
Used plastics such as those which have to be recycled, for example, as a result of the German Packaging Regulation, have an impurity content of up to 10% by weight. Some of these impurities are present as fine fillers and pigments which have virtually no settling rate in the liquefied used plastic. Other inert constituents are, for example, adhering metal parts, for example aluminium lids or thin aluminium layers made of composite foils.
In the preliminary sorting and ancillary processing, it is not possible, or possible only at extremely high expense, to extract these metal foils or to remove them mechanically/manually. At present, the ancillary processing of used plastics permits particle sizes of up to 10 mm. In the extreme case, even metal agglomerates up to this size are therefore possible. The metal parts entrained with the used plastic have, because of their density and sizes, a marked to high sedimentation rate in liquefied plastic. They can therefore erode pumps and other sensitive elements, which may result in their destruction.
In order to be able to depolymerize used and waste plastics thermally, it is necessary to introduce a large amount of energy at a high temperature level (about 400.degree. C.). Plastics are very sensitive to overheating. Such overheating results in uncontrolled decomposition with undesirable side reactions.